Less than two months ago, UKIP caused something of an upset when the party beat the Conservatives into third place at the Eastleigh by-election, and came within striking distance of taking the seat from the Liberal Democrats.[note Fallout from the Eastleigh by-election] With another set of elections just around the corner - a by-election in South Shields and local elections around the country - people are wondering if a repeat performance could be on the cards.

Mid-term elections are often difficult for the government of the day, but I think these may be different, for two reasons. First, the current government is part-way through an unpopular - though they would argue, necessary - austerity programme. Until recently, the government has been able to diffuse some of the dissent by promising that things will get better soon, but meagre growth, rising public debt and the introduction of yet more cuts (in real terms at least) have undermined that argument.

Secondly, the fact that we have a coalition government means that the electorate have to discount two of the three main political parties if they wish to register a protest vote. Whilst Labour should in theory benefit from the absence of the Liberal Democrats in mopping up the anti-government vote, I'm not convinced that the majority of the electorate are willing to support Labour - either because the memory of their economic policy failures are still too strong, or for ideological reasons. That section of the electorate can register their discontent through apathy - not voting or spoiling their ballot - or actively voting for another party. UKIP has three major advantages relative to the other contenders for the anti-politics vote: leadership, reach and respectability.

In terms of leadership - whether you like him or not - Farage has done an exceptional job of raising the profile of the party and making it appear like a mainstream political force. He is forever turning up on BBC Question Time - far out of proportion to UKIP's representation in the country - and his press events are usually packed out. He is also the only minority party leader I can name off the top of my head - and I'm a self-confessed political geek.

When it comes to reach, UKIP is fielding 1,745 candidates - well ahead of the Greens (893), and independents (900).[note Q&A: Local elections 2013] In many wards, if you want to register an active protest vote and can't bring yourself to put a cross next to the Labour candidate, UKIP may be your only option.

Despite some of the comments made by individual members,[note Ukip Candidates: Are 'Clowns' And 'Racists' Attracted To The Eurosceptic Party?] UKIP is not as toxic as the British National Party, nor as outwardly crazy as some other fringe parties.[note If you read the UKIP manifesto, you may find some bizarre policies, but I doubt many people go to those lengths.] Activists in South Shields report that some people are not ready to admit to voting UKIP,[note South Shields voters give Ukip the time of day – but don't tell the neighbours] but so long as they put their cross against the right box on polling day that is all that matters. Furthermore, if the party does gain more representation, that in itself will provide credibility.

The advantage which UKIP has over Labour - as opposed to other minority parties - is that it has never been in government, nor is it ever likely to be. This means that it has not made any decisions which upset people - and decisions made whilst in government always upset some people - plus it can make populist promises on issues such as taxation and tuition fees, safe in the knowledge that it will never have to deliver on them. In many ways, it is in a similar position to the Liberal Democrats before the 2010 general election - although I doubt UKIP will be holding the balance of power in Westminister at any point in the near future.

I am not going to attempt to make a guess at the exact level of suppport for UKIP - either in terms of vote share or seat gains - as they are still an unknown force outside of European elections. I think it is unlikely that they will sweep to victory in South Shields - although Labour's majority may well be reduced - or that they will gain control of a substantial number of councils, but they will probably cause a few upsets along the way. Whatever happens, Friday's results are likely to make uncomfortable reading for at least two of the three main party leaders.